1. Field of the Invention
The present invention relates to a microscope device, and, more particularly, the present invention relates to a microscope device which can selectively use ultraviolet light and visible light as illuminating light.
2. Description of the Related Art
In recent years, semiconductor device structures have achieved increased degrees of miniaturization. For example, in the case of a 16 M dynamic RAM, the line width has become about 0.5 .mu.m.
Microscopes having a high resolving power are necessary in order to observe semiconductor devices having such a fine structure. The use of short wavelength light sources is one way in which to increase resolving power of a microscope. Prior art microscopes have generally used tungsten lamps, halogen lamps, or the like, visible light sources. However, these known light sources do not deliver ultraviolet light. In particular, with respect to extreme ultraviolet light (DUV) having a wavelength of 300 nm or less, the amount of light necessary for observation cannot be ensured.
Mercury lamps, and the like light sources, are used for illumination when ultraviolet light is required for observation. However, the image obtained using a mercury lamp is only a monochrome image, and color information, which is one item necessary for inspection, cannot be obtained. Therefore, even with a microscope device with which observation using ultraviolet light is possible, it is also necessary to be able to perform observation using visible light. However, problems occur with a known illuminating system which illuminates with both ultraviolet light (particularly DUV light) and visible light.
A filter, dichroic mirror, or the like optical element, is used to start to selectively isolate light of some wavelength. It is known to use a visible light illuminating system and an ultraviolet light illuminating system in the same microscope, using this type of optical system.
Because DUV light in particular is harmful to the human body, the microscope device using a DUV light source must have a structure which prevents incidence of the DUV light on the eye, even if by any chance the DUV light should pass through the eyepiece lens of the microscope. However, because the known microscope device having a visible light illuminating system and an ultraviolet light illuminating system in a common observation system light path separates light using a dichroic mirror having predetermined wavelength selectivity, it is difficult to completely separate ultraviolet light and visible light. For example, when a laser or the like is used as an ultraviolet light source, there is a risk that ultraviolet light passes through the dichroic mirror and leaks into the visible light observation system.